A Practical Approach for Estimation of Lateral Load on Piles under Earthquake

ABSTRACT: The problem of lateral load induced on piles under earthquake has been plaguing professional engineers, geo-technical investigators and researchers alike for quite some time. The normal practice is to ensure that the fixed base shear of column does not exceed the static shear load capacity of piles. The inertial and stiffness effect of pile is usually ignored in dynamic earthquake analysis. The present paper proposes a method where based on modal response or time history analysis pile load may be estimated under earthquake, considering its stiffness, inertia and effect of material and geometric damping properties. The results are then compared with the conventional methods. The effect of partial embedment, a situation that may develop under soil liquefaction during earthquake has also been derived. The pile loads are estimated for two cases: 1) When the structure is a lumped mass having infinite stiffness: like a machine foundation or a heavy short vessel supported directly on pile cap. 2) The superstructure has a finite stiffness and mass like a frame (building /pipe rack etc) The paper also suggests a way of how a geo-technical investigator can estimate rationally the dynamic pile loading with minimum information available at the outset of a project. One of the major advantages of the method is that it does not warrant sophisticated software to be developed for this analysis. A simple spread sheet is sufficient to produce an accurate result.